Purification of erythromycin thiocyanate

ABSTRACT

ERYTHROMYCIN THIOCYANATE CAN BE PURIFIED EFFECTIVELY AND ITS POTENCY CAN BE INCREASED SIGNIFICANTLY BY TREATING IT WITH TRICHLOROETHYLENE.

United States Patent 6 3,637,654 PURIFICATION OF ERYTHROMYCINTHIQCYANATE Gerald George Post, Kenosha County, Wis., assiguor to AbbottLaboratories, North Chicago, Ill. No Drawing. Filed Apr. 3, 1969, Ser.No. 813,327 Int. Cl. C07c 47/18 US. Cl. 260-210 E 4 Claims ABSTRACT OFTHE DISCLOSURE Erythromycin thiocyanate can be purified effectively andits potency can be increased significantly by treating it withtrichloroethylene.

Erythromycin thiocyanate is prepared from erythromycin which, in turn,is prepared by fermentation and subsequent extraction. Unfortunately,the extraction methods most practical and most commonly used produce anerythromycin solution which contains a minor amount of fats and oils.These fats and oils find their way into erythromycin thiocyanate fromwhere they cannot be easily removed.

Erythromycin thiocyanate is used as an antibiotic and, in largeramounts, for the preparation of erythromycin base from which variousmedicinal preparations are made, for instance erythromycinethylsuccinate. Thus, large quantities of erythromycin thiocyanate areproduced continuously and unless a substantially pure material isavailable, it cannot be used in the medicinal field. Furthermore,standard processes for the transformation of erythromycin thiocyanate toerythromycin base do not always remove all the fats or oils whichsometimes accompany the thiocyanate so that special procedures have tobe followed subsequently for their removal.

It is therefore an object of the present invention to provide a methodfor the purification of erythromycin thiocyanate; it is a further objectof this invention to provide a simple, inexpensive and fast purificationmethod for erythromycin thiocyanate; it is another object of thisinvention to provide a method for the removal of fats and oils fromerythromycin thiocyanate.

These and other objects are accomplished by slurrying one part by weightof erythromycin thiocyanate in at least two parts by volume oftrichloroethylene for a period sufficiently long to provide intimatecontact between the liquid phase and the solid phase, and recovering theerythromycin thiocyanate from the slurry. Intimate contact betweentrichloroethylene and erythromycin thiocyanate can be provided by anumber of known means, for instance, the erythromycin salt can becontacted with said solvent in a shaking apparatus or by stirring wherebatch operation is desired; however, since the necessary contact time isvery short for effective removal of fats and oils from the erythromycinthiocyanate, a continuous washing method can be devised whereinthe soliderythromycin thiocyanate is forwarded in counter-current flow throughtrichloroethylene by mechanical or gravitational force.

The simple process of the present invention can be carried out attemperatures between and 50 C. or even higher. Excellent results can beobtained at room temperature and therefore heating or cooling are notrequired and can be omitted for most economical operation. The volume oftrichloroethylene is preferably selected between two and three times theweight of the crude erythromycin thiocyanate; however, larger amounts oftrichloroethylene may be used without materially changing the efiiciencyof the present process.

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For better understanding of the process of this invention, reference ismade to the following examples which are merely added as illustrationsand are not intended to limit the invention in any respect.

EXAMPLES 14 Example Before After All numbers given in the above tableare measured as international units per mg. of erythromycin thiocyanate(u./mg.). As seen in the table, the potencies of the samples improvedmaterially by the method used to remove the fats and oils.

EXAMPLE 5 A batch of 10 kg. of erythromycin thiocyanate assaying 690u./mg. was slurried in 25 liters of trichloroethylene for 30 minutes,centrifuged and subsequently washed with 20 liters of trichloroethylene.The material was dried, resulting in 9.5 kg. of purified materialassaying 771 u./mg. The obtained material produced a clear 10% solutionin methanol.

EXAMPLE 6 In a repetition of Example 5, 10 kg. of erythromycinthiocyanate assaying 705 u./mg. were treated with tri chloroethylene,producing 9.2 kg. of the purified material assaying 761 units per mg.

Samples of this same batch of erythromycin thiocyanate were treated inthe above manner prior to drying of the crude precipitate obtained whenan erythromycin solution in isoamyl acetate was precipitated by addingan aqueous solution of ammonium thiocyanate and acetic acid. One hundredgrams of the material obtained after filtration but prior to drying wasslurried in 250 ml. of trichloroethylene, filtered, washed on the filterwith 50 ml. of trichloroethylene and dried. The material thus ob tainedproduced a clear 10% solution in methanol while the material prior toslurrying with trichloroethylene gave a very cloudy solution.

EXAMPLE 7 Erythromycin thiocyanate was prepared by the addition of anaqueous solution of ammonium thiocyanate and acetic acid to an amylacetate extract of the erythromycin fermentation broth. The precipitatewas allowed to settle and the clear solution was decanted. To 400 ml. ofthe resulting slurry was added ml. of trichloroethylene and the mixturewas stirred for 15 minutes before being filtered, washed with 50 ml. oftrichloroethylene and, in turn, with 50 m1. of water. The product wasdried in vacuo at 45 C.; it produced a clear 10% solution in methanolWhereas a control sample which had no trichloroethylene added and waswashed only with an amyl acetate gave a cloudy solution. The potency ofthe treated product was 801 u./mg., while the untreated sample had apotency of 740 u./ mg.

The process of the present invention is specific to trichloroethylene;many other solvents were found to either remove none or onlyinsufiicient amounts of fats and oils to produce a clear 10% methanolsolution, or they resulted in large losses of product due to thesolubility of the erythromycin thiocyanate therein. Trichloroethylenereadily dissolves substantially all oils and fats found in erythromycinthiocyanate prepared in the usual manner; it is inexpensive, relativelynon-toxic, non-inflammable and can be easily recovered by distillation.Trichloroethylene has the further advantage of being easily removablefrom the final product by drying or by washing it out therefrom.

As seen above, the simple procedure of the present invention can becarried out on the dry, crude erythromycin thiocyanate as well as fromthe crude material just precipitated, i.e., without necessitating thecomplete removal of the solvent from the precipitation step in theerythromycin thiocyanate preparation method. The solvents most commonlyused in that step are butyl acetate. methyl isobutyl ketone or isoamylacetate. Remnants of any of these solvents with the crude product do notinterfere with the procedure of the present invention.

I claim:

1. The process of purifying erythromycin thiocyanate consistingessentially of contacting one part by weight of erythromycin thiocyanatewith at least two parts by volume of trichloroethylene for a periodsufliciently long to provide intimate contact between the liquid phaseand the solid phase and separating the liquid phase from the solidphase.

2. The process of claim 1 wherein trichloroethylene is used in an amountbetween 2 and 3 parts by volume per part by weight of erythromycinthiocyanate.

3. The process of claim 1 wherein said erythromycin thiocyanate isslurried in said trichloroethylene for a period of between 5 minutes and1 hour.

4. The process of claim 1 wherein said liquid phase is separated fromsaid solid phase by filtration.

References Cited UNITED STATES PATENTS 2,653,899 9/1953 Bunch et a1.2602l0 E 2,791,531 5/1957 Bellard 26021O E 2,806,024 9/1957 Bird, Jr. eta1. 260210 E 2,864,817 12/1958 Croley 2602l0 E 2,870,138 1/1959 Murray260210 E ELBERT L. ROBERTS, Primary Examiner J. R. BROWN, AssistantExaminer

